Name: generator sequence currents and impedances
Uploaded: 2024-11-21T14:54:31.000Z
Duration: 1 min 24 s
Channel: JoVE

Un generatore sincrono collegato a Y, messo a terra tramite impedenza neutra, è progettato per generare tensioni di fase interne bilanciate con solo componenti di sequenza positiva.
Le reti di sequenza del generatore includono una tensione di sorgente solo nella rete di sequenza positiva e sono illustrati i componenti della sequenza delle tensioni linea-terra ai terminali.
La caduta di tensione nell'impedenza neutra è causata esclusivamente dalla corrente di sequenza zero, l'impedenza neutra in serie con l'impedenza di sequenza zero del generatore.
Nelle centrali elettriche, lo statore del generatore sincrono produce correnti bilanciate trifase a sequenza positiva in condizioni di stato stazionario, generando una forza magnetomotrice netta (MMF) allineata con il rotore.
Con correnti di sequenza negativa trifase bilanciate, l'MMF netto si oppone al rotore, risultando in un'impedenza di sequenza negativa inferiore rispetto all'impedenza di sequenza positiva.
Le correnti di sequenza zero, identiche per grandezza e fase, creano un MMF netto vicino allo zero, rendendo l'impedenza di sequenza zero la più piccola.
Le impedenze di sequenza variano tra le macchine rotanti e sono classificate come sincrone, transitorie o subtransitorie.
Queste reti semplificano il funzionamento dei motori sincroni e asincroni trifase.

reti di sequenza di macchine rotanti

Sequence Networks of Rotating Machines

Un generatore sincrono connesso a stella (Y), collegato a terra tramite un'impedenza neutra, è progettato per produrre tensioni di fase interne bilanciate con solo componenti a sequenza positiva. Le reti di sequenza del generatore includono una tensione di sorgente che è esclusivamente nella rete a sequenza positiva. Le componenti di sequenza delle tensioni linea-terra ai terminali del generatore illustrano questa configurazione.

La corrente a sequenza zero induce una caduta di tensione attraverso l'impedenza neutra del generatore e altre impedenze a sequenza zero nel circuito. Ciò richiede un'impedenza aggiuntiva nella rete a sequenza zero, in serie con l'impedenza a sequenza zero del generatore.

Nelle centrali elettriche, lo statore di un generatore sincrono in condizioni di stato stazionario trasporta correnti trifase bilanciate a sequenza positiva. Queste correnti generano una forza magnetomotrice netta (FMM) che si allinea con la direzione del rotore. D'altro canto, le correnti trifase bilanciate a sequenza negativa nello statore producono una FMM rotante che si oppone alla rotazione del rotore, con conseguente impedenza a sequenza negativa che è in genere inferiore all'impedenza sincrona a sequenza positiva.

Le correnti a sequenza zero, che hanno ampiezza e fase identiche, producono una FMM netta quasi nulla. Di conseguenza, l'impedenza a sequenza zero del generatore è in genere la più piccola tra le impedenze di sequenza.

Le impedenze di sequenza nelle macchine rotanti sono categorizzate in impedenze sincrone, transitorie o subtransitorie. Queste classificazioni aiutano a semplificare l'analisi dei motori sincroni e a induzione trifase utilizzando reti di sequenza.

Reti di sequenza di macchine rotanti

Un generatore sincrono collegato a Y, messo a terra tramite impedenza neutra, è progettato per generare tensioni di fase interne bilanciate con solo ...

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Electrical Engineering

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Unit 1

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Symmetrical and Unsymmetrical Faults

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generator sequence currents and impedances

Generator sequence currents and impedances explain how a Y-connected synchronous generator behaves under balanced and unbalanced conditions. When the generator is grounded through a neutral impedance, it is set up to produce balanced internal phase voltages with only positive-sequence components. The source voltage therefore appears only in the positive-sequence network, and the line-to-ground voltages at the generator terminals show the sequence components of this setup.

Zero-sequence current creates a voltage drop across the generator’s neutral impedance. It also drops voltage across other zero-sequence impedances in the circuit. For that reason, the zero-sequence network needs an added impedance in series with the generator’s own zero-sequence impedance.

In steady-state operation, the stator of a synchronous generator carries balanced three-phase, positive-sequence currents. These currents create a net magnetomotive force, or MMF, that moves in the same direction as the rotor. Balanced three-phase, negative-sequence currents create a rotating MMF that opposes rotor rotation. Because of this, the negative-sequence impedance is usually smaller than the positive-sequence synchronous impedance.

Zero-sequence currents have the same magnitude and phase. They produce almost no net MMF. As a result, the generator’s zero-sequence impedance is usually the smallest of the sequence impedances. In rotating machines, sequence impedances are grouped as synchronous, transient, or subtransient. These categories help simplify the analysis of three-phase synchronous and induction motors with sequence networks.

Generator Sequence Currents and Impedances

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Generator sequence currents and impedances explain how a Y-connected synchronous generator behaves under balanced and unbalanced conditions. When the generator is grounded through a neutral impedance, it is set up to produce balanced internal phase voltages with only positive-sequence components. The source voltage therefore appears only in the positive-sequence network, and the line-to-ground voltages at the generator terminals show the sequence components of this setup. Zero-sequence current...

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Learn how positive-, negative-, and zero-sequence currents shape generator sequence networks, neutral impedance, and MMF in rotating machines.

Generator Sequence Currents and Impedances | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Generator Sequence Currents and Impedances

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